Many electronic devices are sensitive to environmental gases and liquids and are prone to degradation on permeation of the environmental gases and liquids such as oxygen and water vapor. Further, chemicals used in manufacturing and processing of the electronic devices can be harmful to the electronic devices. In order to prevent against this degradation, the electronic devices are usually encapsulated by one or more layers which act as a barrier to harmful gases, liquids and chemicals. Conventionally, the one or more layers used include a flat alternating stack of plastic and inorganic layers. The alternating stack of plastic and inorganic layers prevents the harmful gases, liquids and chemicals from reaching the electronic devices.
However, the barrier layers such as the alternating plastic and inorganic layers being used currently have several disadvantages. For example, the inorganic layers have a much higher e-modulus than the plastic layers. Therefore, on application of mechanical load, the alternating plastic and inorganic layers are stretched and all tension forces are localized on thin inorganic layers, resulting in the thin inorganic layers absorbing much more stress than the plastic layers. Also, the plastic layers and the inorganic layers have different thermal expansion coefficients. Hence, on temperature variations the plastic layers and the inorganic layers behave differently resulting in build up of stress. The thin inorganic layers are not able to withstand the stress and crack thereby resulting in loss of barrier properties.
Hence, techniques have been developed to relieve stress on the inorganic layers. For example, U.S. Pat. No. 6,849,877 provides soft layers between and on top of one or more inorganic layers. According to the invention disclosed in U.S. Pat. No. 6,849,877, stress relief is provided by fracture of a first inorganic layer. Thereafter, the soft layers between the one or more inorganic layers prevent further crack growth into a second inorganic layer. However, the soft layers have no influence on the core problem of fracture proneness of individual inorganic layers under stress.
Additionally, deformation of a substrate adjoining the barrier layers will result in immediate tension or compression and load on the inorganic layers which might cause the barrier layers to fracture and leak.
In light of the foregoing discussion, there is a need for an improved barrier layer that prevents permeability of water, oxygen, harmful gases, liquids and chemicals, and can also withstand mechanical stress, thermal stress and load caused due to deformation of the substrate.